KEYWORDS: 3D image processing, 3D modeling, Phase imaging, Luminescence, Inverse optics, Reconstruction algorithms, Data modeling, 3D metrology, Diffraction, Optical tomography
Phase imaging provides quantitative structural data about biological samples as an alternative or complementary contrast method to the functional information given by fluorescence imaging. In certain cases, fluorescence imaging is undesirable because it may harm the development of living cells or add time and complexity to imaging pipelines. However, current 3D phase reconstruction methods, such as optical diffraction tomography [1], are often limited to a single-scattering approximation. This limits the amount of scattering that such 3D reconstruction algorithms can successfully handle, and therefore effectively limits the sample thickness that can be successfully reconstructed. More recent methods such as 3D Fourier ptychographic microscopy (FPM) have used intensity-only images combined with multiple-scattering models in order to reconstruct 3D volumes [2]. In practice, however, continuous biological samples on the order of 100 um thick are not well-reconstructed by 3D FPM, due to a lack of diverse information across the volume which creates an ill-posed inverse problem. To mitigate this, we introduce simultaneous detection coding in the form of pupil control to the 3D FPM capture scheme. Simple pupil coding schemes enabled us to capture diverse information across our volume. In concert with a beam propagation model that takes into account multiple scattering, this combination of illumination- and detection-side coding allows us to more stably reconstruct 3D phase for larger-scale biological samples.
[1] E. Wolf, “Three-dimensional structure determination of semi-transparent objects from holographic data,” Opt. Commun. 1, 153–156 (1969).
[2] L. Tian and L. Waller, “3D intensity and phase imaging from light field measurements in an LED array microscope,” Optica, 2, 104-111 (2015).
3D quantitative phase (refractive index) microscopy reveals volumetric structure of biological specimens. Optical diffraction tomography (ODT) is a common technique for 3D phase imaging. By angularly scanning a spatially coherent light source and measuring scattered fields on the imaging plane, 3D refractive index (RI) is recovered by solving an inverse problem. However, ODT often linearizes the process by using a weakly scattering model, e.g. the first Born approximation or Rytov approximation, which underestimate the RI and fail to reconstruct realistic shape of high RI contrast multiple scattering objects. On the other hand, non-linear models such as the multi-slice or beam propagation methods mitigate artifacts by modeling multiple scattering. However, they ignore back-scattering and intra-slice scattering and make a paraxial approximation by assuming each slice is infinitesimally thin. In this work, we propose a new 3D scattering model Multi-layer Born (MLB), which treats the object as thin 3D slabs with finite thickness and applies the first Born approximation on each slab as the field propagates through the object, increasing the accuracy significantly. In the meantime, a similar computation complexity is achieved comparing to the previously proposed multi-slice models. Therefore, MLB can achieve accuracy similar to that of FDTD or SEAGLE, a frequency domain solver, with orders of magnitude less computation time. In addition to forward scattering, multiple back-scattering effects are also captured by MLB unlike existing models. We apply MLB to recover the RI distribution of 3D phantoms and biological samples with intensity-only measurements from an LED array microscope and show that the results are superior to existing methods.
We demonstrate three-dimensional (3D) optical phase and amplitude reconstruction based on coded source illumination using a programmable LED array. Multiple stacks of images along the optical axis are computed from recorded intensities captured by multiple images under off-axis illumination. Based on the first Born approximation, a linear differential phase contrast (DPC) model is built between 3D complex index of refraction and the intensity stacks. Therefore, 3D volume reconstruction can be achieved via a fast inversion method, without the intermediate 2D phase retrieval step. Our system employs spatially partially coherent illumination, so the transverse resolution achieves twice the NA of coherent systems, while axial resolution is also improved 2× as compared to holographic imaging.
In this study, we demonstrated an electrically tunable lens coupler for both variable optical attenuation (VOA) and polarization selection. This coupler consists of a liquid crystal (LC) lens sandwiched between two GRIN lens. A GRIN lens is used to couple the light into the single mode fiber, and a LC lens is used to electrically manipulate the beam size of light. It is known that the lens power of a LC lens is tunable with high polarization sensitivity. Then, as the applied voltage on the LC lens is zero, the incident light is focused due to GRIN lens and coupled into the fiber. On the other hand, the beam size of the transformed e-ray becomes larger because the lens power of a LC lens for the e-ray decreases with the increase of the applied voltage. This results in the decrease of the coupling efficiency, and the optical power coupled into the fiber is smaller. This lens coupler for the e-ray functions as a VOA due to a continuous optical attenuation. On the contrary, the lens power of this LC lens for the o-ray does not vary because of optical anisotropy of the LC layer, and then the coupling efficiency for the o-ray remains high. For an arbitrary polarized incidence, this tunable lens coupler acts as a broadband polarizer for the fiber systems. The polarization dependent loss is larger than 30 dB and the switching time is around 1 second.
We demonstrate a hysteresis-free PSBP-LCs by inveistagating crystal growth and phase separation process of PSBP-LCs. By enlarging the domain size and uniformity of the crystal orientations of PSBP-LC, the hysteresis of PSBP-LCs can be eliminated. The large domain size and uniform crystal orientations of PSBP-LCs reduce the mismatch of the crystal orientations of PSBP-LCs. Based on this study, we also demonstrate a hysteresis-free electro-optical switch using dye-doped PSBP-LCs. Hysteresis-free PSBP-LC is important in many applications, such as displays, electro-optical switches, and electrically tunable focusing lenses.
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